1. Field of the Invention
The present invention relates to a zoom lens and an imaging apparatus, and specifically relates to a zoom lens that are small and light weight and have a hand-shake compensation function and an imaging apparatus.
2. Background Art
In a zoom lens for a single-lens reflex camera in the conventional technology, long flange focal length against a focal distance has been required to distribute an optical element relating to an optical viewfinder. Therefore, the long flange focal length has been secured through a lens design in which a lens group having a positive refractive power is arranged in a backward lens group disposed on the image focusing side among lens groups constituting the zoom lens to ease securing of the proper back focus. However, in recent years, depending on miniaturization of an imaging apparatus body and/or the popularization of a digital still camera employing a live view imaging on the liquid crystal display provided on the back of the imaging apparatus body, an imaging apparatus not provided the optical viewfinder has been widely used. Therefore, zoom lenses not require the long flange focal length increase, and the miniaturization of the zoom lens is demanded. In such a small zoom lens, a zoom lens suitable for video imaging including the zoom lens having a miniaturized focusing lens group and/or a vibration-compensation lens for hand-shake compensation have been proposed.
Especially in an automatic focusing at high speed in video imaging, repeated sequential motions including: vibrating (wobbling) of a part of lens groups (focusing lens group) at high speed in the optical axis direction to perform non-focusing/focusing/non-focusing state; detection of a signal of a certain frequency band of a partial image area from an output signal from an imaging sensor; determination of an optimal position of the focusing lens group in the focusing; and moving the focusing lens group to the optimal position; may be applicable. If wobbling is employed in the zoom lens design, the matter should be noted that the size of an image corresponding to the object changes in wobbling. Such magnification change in focusing depends on a change of the focal distance in the entire lens system by moving the focusing lens group in the optical axis direction in wobbling. For example, in live view imaging, if magnification change is large in wobbling, the user feels something wrong. To reduce something wrong, focusing by a lens group backward than a diaphragm is known to be effective. In addition, downsizing of the focusing lens groups is essential for wobbling with high-speed auto focusing.
Thus, not only miniaturization of a zoom lens depending on miniaturization of an imaging apparatus and the short flange focal length in recent years but also reduction in both the outer diameter of focusing lens groups and the weight as much as possible to drive the focusing lens group high speed are demanded.
Also in a vibration-compensation lens group, reduction in both outer diameter and weight is demanded to achieve not only reduction of the influence on image degradation due to hand-shaking but also reduction of the load on a vibration-compensation drive system.
Under such technical background, for example, Japanese Patent No. 3958489 discloses a wide-angle high-magnification zoom lens composed of five group lenses of a positive, negative, positive, negative and positive arranged from the object side. Further, Japanese Patent No. 2773131 discloses a compact high-magnification change zoom lens and proposes an optical system arranged a positive, negative, positive, negative and negative in Example 7. Furthermore, Japanese Patent Laid-Open No. 2011-247962 discloses a high-magnification change zoom lens and proposes an optical system arranged a positive, negative, positive, negative and negative in Example 2.